THE GULLS 249 



The great disparity between these figures cannot be due entirely 

 to specific variations — there must be faulty estimating. This is indicated 

 when we compare the above estimate for the kittiwake by Jourdain 

 with two accurate records of the fledging period of this species : 44 and 

 45 days (Keighley and Lockley, 1947). There is plenty of room for 

 more exact observation. 



Literature dealing with the period between the time when the 

 gull chicks are fledged and their dispersal to winter quarters is scanty. 

 At Skokholm, Lockley (1947) found that the adult great black-backs, 

 the lesser black-backs and the herring-gulls gradually left the island 

 in August, September and October, and a small number of the fully 

 fledged young gulls appeared to leave at the same time. But many of 

 these juveniles were left behind, and there were periods when the 

 island held about one hundred juveniles and few or no adults. In 

 calm weather these juveniles managed to get a living by wandering 

 about the island picking food from the surface of the land, including 

 food obtained from the carcases of dead puffins, shearwaters and rabbits, 

 and along the tide-line. But in stormy weather, which was frequent 

 in autumn, many of the young gulls whose powers of flight seemed 

 feeble, would remain in a loose flock in the centre of the island, 

 mewing a great deal as if hungry, but unwilling to fly in search of 

 food. It was found that many of these birds were thin and generally 

 in very poor condition ; and if the weather continued rough some of 

 them died or grew so feeble that they could easily be run down and 

 caught in the open. 



Comparative figures from other gulleries reveal that an extremely 

 small proportion of chicks is raised each season, due to egg-stealing, 

 cannibalism, and other factors, including rough weather at fledging 

 time. Paludan (1951) records only 20% chicks fledged in herring- 

 gulls and 5% in lesser black-backs on an island near Bornholm in the 

 Baltic. The possibility of disease attacking young gulls in crowded 

 colonies should also be borne in mind; it may have been the cause of 

 the enfeeblement of so many of the young gulls at Skokholm, where, 

 in August 1947, three juvenile herring-gulls died after a few days of 

 sickness. Examination of the corpses revealed that all three had 

 blistered feet, a characteristic feature of an epizootic which has caused 

 the death of many juvenile Manx shearwaters in the autumn on Skomer 

 and Skokholm (Surrey-Dane, 1948). 



It is doubtful if juvenile gulls remain attached to the adults for 

 long in the autumn. They do, however, frequently follow adults. 



